Conventionally, liquid crystal display elements, which are made by bonding a paired substrates to each other with their electrode-bearing surfaces facing inside and by sealing liquid crystal into the gap between them, have been well known. In such liquid crystal displays, when the distance between the opposing substrates varies due to deformation of the substrates caused by external pressure or other adverse effects, changes in the threshold-voltage value of switching, shortcircuit in the electrodes between the opposing substrates, disturbance in the orientation of the liquid crystal molecules, etc. tend to occur, thereby making it impossible to provide good display images. For this reason, in order to keep the distance between the paired substrates constant, some methods for placing spacers between the substrates have been suggested; conventionally, either of the following two methods is commonly adopted: (1) a method for spraying spherical particles and (2) a method for forming pillars made of an organic or inorganic material.
Specific examples of method (1) include a dry method in which spherical fine particles, made of, for example, an organic resin, such as a polymer of divinylbenzenes, are dispersed in a gas flow of nitrogen and are sprayed on the substrates, and a method in which the spherical fine particles are mixed in an alcohol solution or other solutions and sprayed on the substrates in a mist state.
However, method (1) has the following problems: the first problem is that since the fine particles have a coagulating property whereby they coagulate with one another, it is difficult to spray them on the substrates in a uniform manner and consequently to achieve a uniform cell thickness. The second problem is that since it is difficult to control the adherence location of the fine particles, the particles, which have been unintentionally sprayed on pixel portions, tend to cause defects in the orientation, resulting in low display quality. Further, the third problem is that since the substrates are supported by the spherical fine particles that function as spacers only at their contact points, it is difficult to obtain sufficient strength against external pressure.
Moreover, method (2) more specifically refers to a method in which: an organic or inorganic film is formed with a predetermined thickness, a resist film is formed thereon, and the resist film is irradiated by ultraviolet lights using a photomask, thereby forming pillars that function as spacers. Here, instead of the resist film, for example, photosensitive organic resins, such as photosensitive polyimide or photosensitive acryl resins, can be adopted.
As described above, advantages of method (2) are that the pillars can be selectively formed on the outside of the pixels, and that the contact surfaces between the substrates and the pillars can be shaped into a desired pattern. Thus, method (2) is superior in the uniformity of the cell thickness, the strength against external pressure, and the display quality, as compared with method (1).
Recently, ferroelectric liquid crystal has been taken notice of as a prospective liquid crystal material since it has superior properties, such as having spontaneous polarization and providing high-speed response. However, the disadvantage of ferroelectric liquid crystal is that since it has a structure whose molecule-regularity is closer to that of a crystal, once the molecular orientation has been disturbed, it is difficult to return to its original state, that is, it is susceptible to shock. For this reason, in order to solve the above-mentioned inherent problem with ferroelectric liquid crystal, it is essential to provide a substrate construction that is superior in shock resistance. In order to provide a method for manufacturing such a liquid crystal display element, the method (2) is considered to be a more prospective candidate than the method (1).
However, in recent years, liquid crystal display elements have been required to meet further demands for display with high-resolution and large capacity; the required electrode gap on the substrate surfaces is as small as approximately 20 .mu.m. Accordingly, the conventional method, in which insulating films are formed as spacers between the adjacent electrodes by exposing a photosensitive resin from the upper-surface side of the substrate using photomasks, has a problem in which extremely high definition is required in positioning the mask patterns and photomasks.
If the precision is low, gaps tend to be formed between electrodes 72 and an insulating film 73, for example, as illustrated in FIGS. 9(a) through 9(c). Here, in FIGS. 9(a) through 9(c), reference number 71 represents an insulating substrate, and reference number 74 represents a photomask. In such a case, a black matrix needs to be formed in order to prevent leakage of light from the gap between the electrodes 72 and the insulating film 73, or the aperture rate tends to be reduced due to the unwanted formation of the insulating film 73 on the electrode 72, as illustrated FIGS. 9(b) and 9(c), thereby resulting in other problems.
In order to solve the above-mentioned problems, for example, Japanese Examined Patent Publication No. 41810/1992 (Tokukouhei 4-41810) discloses a method for forming insulating films without using photomasks. In this method, as illustrated in FIG. 10(a), an organic resin film 83 of a photosensitive type is first formed in a manner so as to cover a transparent substrate 81 and a plurality of transparent electrodes 82 that have been formed thereon. Then, the organic resin film 83 is exposed by irradiating it with ultraviolet light from the rear-surface side of the transparent substrate 81. Here, filters are stacked on the transparent electrode 82, if necessary.
As a result, the transparent electrodes 82, or the transparent electrode 82 and the filters, function as photomasks, and when non-exposed portions of the organic resin film 83 is removed by an etching process, the remaining portions of the organic resin film 83 are formed in an adjacent manner to the transparent electrodes 82 without gaps, as illustrated in FIG. 10(b).
However, the problems with a construction manufactured by the above-mentioned method are that defects in the orientation tend to occur in the vicinity of the spacers since the organic resin film 83, which functions as spacers, is adjacent to the transparent electrodes 82, and that display nonuniformity tends to occur since differences are likely to occur in the switching characteristics of the liquid crystal between the vicinity of the spacers and the center portions of pixels. Moreover, in order to allow the transparent electrodes 82 to function as photomasks even in the case when filters are formed on the surfaces thereof, it is necessary to limit conditions upon exposure of light, such as the wavelength and intensity of light to be applied, to an extremely narrow range. This raises another problem in which the material of the organic resin film 83 is limited to a material that can be cured under the above-mentioned limited conditions.
In addition to the above-mentioned example, Japanese Examined Patent Publication No. 41809/1992 (Tokukouhei 4-41809) discloses another method in which: light-shielding films are first selectively formed on a transparent substrate, a light-transmitting organic resin film is next formed thereon, a positive-working photoresist film is further formed on the resin film, the photoresist is formed into a predetermined shape by irradiating it with light from the rear-surface side of the transparent substrate using the light-shielding films as a mask, and the resulting photoresist is used as masks so that the organic resin film, which is located beneath them, is formed into a predetermined shape; thus, spacers are formed. However, even in a construction manufactured by this method, since spacers are formed in an adjacent manner to the pixel display sections, the same problems as described above, that is, defects in the orientation in the vicinity of the spacers and the ununiformity in the switching characteristics, have been raised.